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Summary of South Pacific Tsunami Events 2009

Background Information

Sunday, January 1, 2012

NOAA National Geophysical Data Center

Comments for the Tsunami Event - from NOAA Geophysical Data Center

Felt Reports

At least 149 people killed in Samoa, 34 killed in American Samoa and 9 killed, 7 injured and 500 displaced on Niuatoputapu, Tonga. Widespread damage to infrastructure occurred at Pago Pago, American Samoa, in many parts of Samoa and on Niuatoputapu, Tonga. Nearly all of the casualties and damage was caused by large tsunamis, with run up heights of 12 m at Poloa, 7 m at Pago Pago and Tula, American Samoa and 3 m on Niuatoputapu. Felt (V) at Apia, Samoa and (IV) at Ili`ili and Tafuna, American Samoa. Felt in much of American Samoa, Samoa and northern Tonga and as far away as Wallis and Futuna Islands. The tsunami was recorded with the following wave heights (peak-to- trough) on these selected tide stations: 411 cm at Pago Pago, American Samoa; 140 cm at Apia, Samoa; 111 cm at Rarotonga, Cook Islands; 64 cm in the Chatham Islands, 37 cm at Raoul, 21 cm at Tauranga, 14 cm at Gisborne, 11 cm at Wellington, New Zealand; 28 cm at Nuku`alofa, Tonga; 29 cm at Papeete, French Polynesia; 25 cm at Luganville, Vanuatu; 36 cm at Honolulu, Hawaii; 22 cm at Point Kemblao, Australia; 66 cm at Crescent City and 26 cm at Los Angeles, California; 42 cm at Cabo San Lucas, Mexico; 11 cm at Old Harbor and 4 cm at Seward, Alaska; 36 cm at Ofunato, Japan; 27 cm on Baltra, Ecuador; 73 cm at Antofagasta and 40 cm at Valparaiso, Chile.

Tectonic Summary

The broad-scale tectonics of the Tonga region are dominated by the relative convergence of the Pacific and Australia plates, with the Pacific plate subducting westward beneath the Australia plate at the Tonga trench. At the latitude of the earthquake of September 29, 2009, the Pacific plate moves westward with respect to the interior of the Australia plate at a velocity of about 86 mm/year. The earthquake occurred near the northern end of a 3,000 km long segment of the Pacific/Australia plate boundary that trends north-northeast.; farther north of the earthquake’s source region, the plate boundary trends northwest and then west. The eastern edge of the broad Australia plate may be viewed as a collection of small plates or microplates that move with respect to each other and with respect to the Pacific plate and the Australia plate interior.

On the basis of currently available location and fault mechanism information, we infer that the September 29 earthquake occurred as a normal fault rupture on or near the outer rise of the subducting Pacific plate.

The broad-scale Australia/Pacific plate boundary is one of the most active earthquake regions in the world. Earthquakes occur on the thrust-fault boundary between the Australia and Pacific plates, within the Pacific plate on both sides of the trench, and within and on the boundaries of the small plates that compose the eastern edge of the overall Australia plate.

(above from reference #1053)

Samoa: The official death toll stands at 143, with five people missing. An estimated 4,500 people have been directly affected by the tsunami, most of who are displaced. Tonga: Nine people died and seven were seriously injured as a result of the tsunami that struck the northern island of Niuatoputapu. The Government has released its disaster assessment report and estimates the total cost of damage as Tongan Pa’anga 18.2 million (approximately US$9.5 million). (reference #8715)

148 killed, 5855 affected, $150 million damage. (reference #1250)

The present, and probably definitive, human death toll is 34 on American Samoa, 146 in (independent) Samoa, and 9 on the Tongan island of Niuatoputapu, for a total of 189 persons killed. Economic losses are estimated conservatively at US$200 million. (reference #8422)

Since the disaster declaration more than 11 months ago, federal assistance to American Samoa, including FEMA’s operational expenses, has exceeded $125.5 million, and an additional $4.3 million is planned for future distribution.(reference #9056)